Direct measurement of electron Bernstein waves in Low Aspect ratio Torus Experiment (LATE)

Abstract

By using a newly developed five-pin probe antenna and two-dimensional mechanical probe driving system, the 2-D wave pattern of phase and amplitude has been directly measured in Low Aspect ratio Torus Experiment (LATE), for an overdense ECR plasma with microwave obliquely injected. In the case of O-mode injection, an EBW-like wave pattern has been detected for the first time, in a localized region near the upper hybrid resonance layer. The pattern has a short wavelength of about 2 mm and is also electrostatic and backward. In the case of X-mode injection, the 2-D wave pattern is quite different and no EBW signal can be observed. By adjusting the toroidal magnetic field in O-mode injection, it is found that both the position and size of the EBW region have changed, which suggest the localized condition of efficient O-X-B conversion and high collisional damping rate of EBWs in these experiments.

A radiometer to diagnose parametric instabilities during linear excitation of electron Bernstein waves in the Mega Amp Spherical Tokamak (MAST) Upgrade

“…The scheme is illustrated in figure 1. The O-X-B scheme has been the subject of a number of low power EBW heating and current drive experiments 1,2,5 and recently the excited EBW was measured directly using a probe 6 in the LATE device. The O-X-B scheme has the potential to provide a method for microwave based heating and current drive in overdense plasmas which is often the case in spherical tokamaks.…”